The present invention relates to an improved mechanism for connection to an actuator for a valve or a choke which can be operated mechanically to cause the reversal of the position of the valve member.
U.S. Pat. No. 4,194,718 Baker et al is an example of the prior are of such override mechanisms as applied to a choke and which can be operated by a handwheel. It includes means for releasably connecting the manual operator to the gate to manually move the gate and for releasing the manual operator from the gate to allow such movement.
U.S. Pat. No. 3,378,224 to Boyle discloses a gate valve which is piston actuated together with a handwheel having a sleeve threaded on the shaft which extends through the piston. Rotation of the handwheel causes movement of both the piston and the valve member.
U.S. Pat. No. 4,189,980 discloses a manual control apparatus which has a split drive nut and a camming system which coacts with the rotation system for bringing the split drive nut into engagement with the threaded drive screw and rotating the split nut to move the drive screw and the valve member connected thereto.
U.S. Pat. No. 3,628,397 discloses a valve member having a ball nut secured to the upper portion of the piston and a ball shaft secured to the top of the bonnet and mounted so that its rotation causes movement of the piston and valve member. During normal operation, movement of the piston will cause rotation of the ball shaft.
U.S. Pat. No. 4,213,480 discloses an override mechanism for a valve in which a nut is threaded onto the drive stem and is engaged by a drive sleeve which telescopes onto the nut and splines connect the sleeve to the nut. Rotation of the sleeve rotates the nut which contacts one of the abutment surfaces and then causes movement of the gate.